Drop legs for compressed air lines

ABSTRACT

A drop leg has a housing provided with top and bottom ends. The top end has an inlet and an outlet and the bottom end has a drain. An impingement plate supported within the housing is spaced from the top end to establish a separating chamber and to be directly contacted by the air stream through the inlet. The upper surface of the impingement plate is downwardly and inwardly inclined and has a central drain. The air stream striking the inclined surfaces rebounds towards the outlet. When vapors are also present, the drop leg is provided with a bulkhead which is sealed to the housing and establishes with the impingement plate an upper chamber and with the bottom end a settling chamber for contaminants separated from the air stream. The space between the periphery of the impingement plate and a portion of the housing establishes an orifice which may be adjustable, enabling a limited volume of air to escape into the upper chamber and thence to atmosphere with a resulting pressure drop effecting the cooling of the impingement plate to assist in the separation of vapors and other contaminants from the air stream.

BACKGROUND OF THE INVENTION

The importance of assuring that compressed air is as clean and dry aspossible before using it in any type of application is universallyappreciated. The process of compressing air not only concentratesimpurities in the atmosphere, but adds many more, rendering the finalproduct totally unacceptable for many of the very wide range ofapplications involving the use of compressed air.

There are many divergent methods available to remove contaminates fromcompressed air and most of them consist of passing the air through abarrier. The barrier may be chemical or mechanical, but it will alwayshave a limited period of effectiveness, the period being governed by thetime it takes to become saturated with contaminates. When this happensthe barrier must be cleaned or replaced, involving maintenance time andcosts, or the contaminates will be forced into the air line. Anythingwhich will prolong the effectiveness of the barrier is not only a costsaver but also an assurance of a more consistant supply of properlyfiltered air.

The most basic and effective method of removing the bulk of contaminatescarried in an air flow is the use of a drop leg. This strictlymechanical device never clogs up, never wears out and, apart from havingto have the accumulation of contaminates drained off, requires nomaintenance. It uses a natural phenomena of air flow to separate gas andcontaminate molecules and the greater the flow, the more efficient itbecomes.

Drop legs have been in use since the first compressed air lines wereinstalled. They originated in a similar capacity for steam lines andwere converted to use with compressed air without any major changes.Their effectiveness is qualified by the fact that most suppliers ofpneumatic equipment, including filters and dryers, recommend that a dropleg be installed prior to their equipment.

A conventional drop leg consists of a single tube carried past the pointof take off of an air drop, an air drop merely being the pipe whichcarries the air down to working level from the overhead main pipe, or"leader". The diameter of the down pipe is usually expanded below thetake-off point, capped and fitted with a drain cork. These legs functiondue to the fact that air molecules travel in a straight line and, havingbeen directed into a flow path by the down pipe, continue in that pathuntil they impinge on the cap at the base of the tube. The gas moleculesrebound and continue to move with undiminished energy, but anythingwhich has no energy of its own, usually such as water, dirt and oil, isleft at the point of impingement.

This is, of course, a "catch as catch can" arrangement and rapidly losesits original efficiency when any accumulation of contaminates occurs.The turbulence then actually re-introduces the lighter contaminatematter into the air flow, leaving only the heavier matter at the base ofthe tube. This is evident when draining a drop leg and a heavy sludge isdrawn off. Nevertheless, this is the very stuff which is most dangerousto filter screens and tools so the leg serves a very worthwhile purpose.

It has been proposed to provide drop legs with a separate air outlet. Asfar as we are aware, such air outlets have required the air, afterstriking the impingement surface to pass downwardly below that surfacein a turbulent manner such as to cause reentry into the outlet airstream of at least the lighter contaminants which may have been removed.See U.S. Pat. Nos. 2,467,408 and 3,345,807.

THE PRESENT INVENTION

The general objective of the present invention is to provide drop legsfor compressed air lines of greatly increased efficiency in removingcontaminants from the air.

In accordance with one aspect of the invention, this objective isattained with drop legs each of which has an outlet above theimpingement surface to receive directly rebounding air and continue itsupward course and at the same time draining separated contaminants intoa zone isolated from turbulence. Each such drop leg has a straight inlettube disposed to discharge air downwardly against the impingementsurface and of sufficient length to ensure that the air molecules andentrained matter are all travelling in a straight line, the tube lengthapproximately fifteen times the internal diameter of the tube. Bestresults are attained with the impingement surface inclined inwardly anddownwardly in a manner such that rebounding air is directed generallytowards the outlet. In practise the outlet is a straight length oftubing which may include a filter. The upper ends of the inlet andoutlet tubes are held by a yoke.

While such drop legs effectively collect contaminate matter, matter invapor form presents a problem and another aspect of the invention is theprovision of drop legs which also enable such vapors to be removed. Tothat end, the drop leg has an impingement plate which is a free fitwithin the housing and a bulkhead below the impingement plate which issealed to the housing and establishes an upper chamber vented to theatmosphere and a lower chamber. The drain opens into the lower chamber.The periphery of the impingement plate and the housing establish anorifice such that air can flow into the upper chamber but with anattendant pressure drop thus effecting the cooling of the impingementplate, condensing water vapor and coalescing oils. Where required, thedimensions of the orifices of such drop legs may be varied.

Another objective of the invention is to provide a housing well suitedfor drop legs of either of the above types. In accordance with thisaspect of the invention, the housing consists of a length of tubing andupper or top and lower or base plates dimensioned to fit in the ends ofthe tube to the extent permitted by shoulders with which the end platesare formed. A tie rod extends axially through the tubing and one end isthreaded into and sealed to the top plate and its other end extendsfreely through and is sealed to the base plate against leakage. A nutthreaded on the exposed end of the bolt holds the assembly together.

Where only an impingement plate is needed, the plate has an axial boreto receive the tie bolt and where a bulkhead is also required an axialbore for the tie bolt extends through both the impingement plate and thebulkhead.

Another objective of the invention is to combine the impingement plateand the bulkhead into a module including a support to seat on the baseplate with the drain an axial passageway through the module freelyreceiving the tie bolt.

Another important objective of the invention is to provide for theadjustment of the dimensions of the orifice. An objective attained byproviding the tube with a step overlying the periphery of theimpingement plate and defining therewith the orifice and by providingmeans to effect the movement of the impingement plate towards or awayfrom the step to effect wanted changes in the dimensions of the orifice.A particular objective is to utilize the tubular housing and a module,both described above with a compression spring between the impingementplate and the top plate of the housing to hold the module seated againstthe bottom plate. The bottom plate and the bulkhead are slidably sealedto the housing. Accurate adjustments of the orifice are effected byutilizing the turning of the tie bolt nut in one direction to permit theslight movement of the base plate away from the top plate required toenable the spring to effect the slight repositioning of the impingementplate and in the other direction to advance the base plate towards thetop plate against the resistance of the spring to effect the wantedrepositioning of the impingement plate.

Other objectives of the invention and the manner in which they areattained will be apparent from the description of presently preferredembodiments and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate presently preferred embodiments ofthe invention of which

FIG. 1 is a vertical section, on an increase in scale, of a drop legfilter in accordance with one such embodiment of the invention with theinlet and outlet tubes broken away to foreshorten the figure;

FIG. 2 is a side elevation of a drop leg filter in accordance withanother such embodiment; and

FIG. 3 is a section taken substantially along the indicated line 3--3 ofFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiment of the invention illustrated by FIG. 1 has a housing,generally indicated at 5, shown as consisting of a tube 6, an upper ortop end plate 7 and a bottom end or base plate 8. The end plates aredimensioned to fit within the ends of the tube 6 and are provided withseals 9 and formed with shoulders 10 against which the ends of the tube6 may be seated. The housing 5 is completed by a tie bolt 11 whichextends axially through the tube 6 with one end threaded in and sealedto the upper end plate 7 and the other end extending freely through thebottom end plate 8 and provided with a seal 12. A nut 13, such as anelastic or self locking nut, is threaded on the exposed end of the bolt11 into contact with the bottom end plate 8 until the shoulders 10 buttagainst the ends of the tube 6. It is important to note that the housingwill remain assembled if the nut 13 is backed off to a limited extent asthe seals 9 will then frictionally hold the tube 6.

The top plate 7 has ports 14 and 15 which are located on opposite sidesof the center line of the housing 5. A straight rigid tube 16 is sealedin the port 14 with its upper end extending through a yoke 17 andprovided with a fitting 18 for use in connecting to it the upstreamsection, not shown, of a compressed air line. The length of the tube 16is such that the molecules of and entrained matter in the air streamdischarged into the housing 5 will be travelling in straight lines. Aset screw 19 serves to lock the yoke 17 to the tube 16.

A like but somewhat shorter tube 20 is secured in the port 15 with itsupper end sealed in a bore 21 in the yoke 17. The yoke 17 has alaterally opening port 22 which intersects the bore 21 and isdimensioned to enable the downstream section, not shown, of thecompressed air line to be coupled thereto.

A module, generally indicated at 23, is confined within the housing 5and includes an impingement plate 24 having a downwardly and inwardlyinclined surface 25 directly exposed to the ports 14 and 15 and spacedfrom the top plate 7 to establish a separating chamber, generallyindicated at 26. The impingement plate 24 is a free fit within thehousing to provide an orifice 27. The module 23 also includes a bulkhead28 provided with a seal 29 and is a sliding fit in the tube 6. Themodule has an axial hub 30 which extends below the bulkhead 28 and restson the bottom plate 8. The bulkhead 28 thus establishes with theimpingement plate 24 an upper chamber, generally indicated at 31 andwith the bottom plate 8 a lower chamber, generally indicated at 32. Thetube 6 has vents 33 opening from the upper chamber 31 to atmosphere. Thehub 30 has an axial bore 34 which freely receives the bolt 11 andestablishes a drain leading from the center of the surface 25 andopening through ports 35 into the lower chamber 32 which serves as asettling chamber for separated contaminants.

The tube 6 is provided with an internal step 36 in the separatingchamber 26 which overlies the upper periphery of the impingement plate24 to define therewith an annular orifice 37 dimensioned to permit alimited air flow from the separating chamber 26 into the subjacentchamber 32 such that it is attended by a pressure drop and the resultantcooling of the impingement plate 24 and also the bulkhead 28.

The downwardly and inwardly inclinded surfaces 25 are directly exposedto the inlet air stream with the inclination of the now cooled surfacessuch that the air stream rebounding from them is directed generallytowards the outlet port 15 with separated particles and condensatesentering the bore 34, the effective dimensions of which are the annularspace surrounding the tie bolt 11, and discharged into the settlingchamber 32 which is either continuously or periodically drained througha port 37 provided in the bottom plate 8.

As the disclosed embodiments provide for the adjustment of the orifice37 as required by operating conditions, the dimensions of the orifice 27may be relatively large. Adjustments of the orifice 37 are effected bysmall axial adjustments of the position of the module 23 and accordinglyof the impingement plate 24 relative to the step 36 to decrease or widenthe orifice 27. For that purpose, a compression spring 39 in the chamber26 surrounds the bolt 11 and is seated on the surfaces 25 of theimpingement plate 24 close to the drain and is backed by the top plate 7between the ports 14 and 15.

By turning the tie bolt nut 13 in the loosening direction, the spring 39is operable to force the module 23 and the end plate 8 away from the topplate 7 and by turning the nut 13 in a tightening direction, the baseplate 8 and the module 24 are moved against the resistance of the spring39 towards the top plate 7 thus enabling fine adjustments of the orificeto be accurately made.

As the embodiment of the invention illustrated by FIGS. 2 and 3 isgenerally similar to that illustrated by FIG. 1, only different or addedfeatures will be detailed but corresponding parts are identified by thesame reference numerals distinguished, however, by the suffix addition"A".

In FIGS. 2 and 3, the outlet tube 20A is of reduced length and isconnected to the base plate 40 of a filter, generally indicated at 41.

The yoke 17A has a vertical bore dimensioned to receive a holder 42having an end extending below the yoke 17A and provided with a socket 43intersected by the laterally opening outlet port 44 on opposite sides ofwhich there are seals 45 carried by the holder 42.

The filter 41 consists of a tube 46 with the base 40 and an annular head47 fitted within and sealed thereto. The head 47 fits on the exposed endof the holder 42 and into an annular seat 48 surrounding the lower endof the bore 41.

A filter element 49 surrounds and is spaced from a supporting tube 50having lengthwise slots 51 with one tube end within the socket 43 andits other end supported by a headed connector 52 seated in and closingan axial bore 53 in the base plate 40. It will be noted that the outlettube 20A opens into the filter 41 at one side of the filter element.

From the foregoing, it will be apparent that drop legs in accordancewith the invention, with or without filters are not only extremelyefficient in use but also are well adapted to meet manufacturingrequirements.

I claim:
 1. A drop leg to be incorporated in a compressed air line, saidwater leg including a housing having top and bottom ends, the top endhaving an inlet and an outlet, the bottom end having a drain, animpingement plate within the housing and spaced from the top end toestablish a separating chamber and directly exposed to the inlet andoutlet, the upper surface of the impingement plate downwardly andinwardly inclined towards the center thereof, the inlet and outlet portsare located on opposite sides of said center and the inclination of saidsurface such that the air stream through the inlet after striking saidsurface rebounds generally towards the outlet, and the impingement platehas a drain adjacent the center thereof and in communication with thedrain in the bottom end.
 2. The drop leg of claim 1 in which the inletis a straight length of tubing the minimum length of which isapproximately fifteen times the tube internal diameter to insure thatthe air molecules and entrained matter travel along straight paths. 3.The drop leg of claim 1 in which the outlet includes a filter and a yokeconnects the outlet and the inlet.
 4. The drop leg of claim 1 in whichthe impingement plate is spaced above the base plate to establish asettling chamber into which the drain opens.
 5. The drop leg of claim 1in which the impingement plate is a free fit within the housing, meansconnected to an end of the housing support the impingement plate, abulkhead between the impingement plate and the bottom end is sealed tothe housing and establishes with the impingement plate an upper chamberand with the bottom end a lower chamber, the housing has vents openingthe upper chamber to the atmosphere, the periphery of the impingementplate and the housing establish an orifice dimensioned to permit limitedair flow from the separating chamber into the upper chamber with anattendant pressure drop to effect the cooling of the impingement plate,and the drain of the impingement plate is a conduit opening into thelower chamber.
 6. The drop leg of claim 5 in which the housing has amarginal portion overlying the periphery of the impingement plate toestablish the orifice.
 7. The drop leg of claim 6 in which thesupporting means is adjustable to enable the relationship between theimpingement plate and the marginal portion to vary the dimensions of theorifice.
 8. The drop leg of claim 5 in which the housing includes atubular member provided with a marginal portion overlying the peripheryof the impingement plate to establish the orifice, the bottom end andthe bulkhead are slidably sealed to the tubular member, adjusting meansconnecting the top and bottom ends to the tubular member, the adjustingmeans connecting the bottom end to the tubular member so that the bottomend may be moved towards and away from the top end while slidablyattached to the tubular member, the impingement plate includes adepending central support resting on the bottom end, resilient meansbetween the upper end and the impingement plate yieldably maintains thesupport seated on the bottom end, operation of the adjusting means toeffect movement of the bottom end attended by corresponding movement ofthe impingement plate and a change in the dimensions of the orifice. 9.The drop leg of claim 8 in which the drain conduit extends through thesupport.
 10. The drop leg of claim 9 in which the means connecting thetop and bottom ends to the tubular member includes a tie bolt extendingfreely through the bottom end, the support of the impingement plate andhas one end threaded into the top end with the other bolt end exposed onthe outside of the bottom end to be engaged and turned in one directionor the other, in one direction enabling the resilient means to move theperiphery of the impingement plate away from the overlying marginalportion of the housing and in the other direction overcoming theresistance of the resilient means and moving said periphery towards saidmarginal portion.
 11. The drop leg of claim 10 in which the impingementplate, bulkhead, and support are components of a module and the bulkheadis slidably sealed to the tubular member.